I think it depends on what Air Transat do for next summer. They served Athens this summer, but I have not seen where they have committed to Athens for 2011.

Montreal-Paris should be no problem with XL, Corsairfly, Air France, Air Canada, Air Transat all competing on that route.

So I’m thinking YUL-PAR with one of these, and ATH-YUL with Air Transat—if they serve it again. Otherwise, you could just do YUL-PAR round trip, and add ATH-PAR with Easyjet.

I’m the last person to go against any advice Don gives on flights but check out flying to Frankfurt, Amsterdam and/or Brussels. They might be cheaper and the TGV can get you to Paris in no time at all.

I think Don’s advice will work out !!
I found a round trip Montreal – Paris for only 800 $ !!
But Easyjet does not have the prices for mid may 2011 yet. Should I book my Athenes – Paris flight in Europe ?? With a local company ??

I would bet that Easyjet will renew the route. Like many low-cost airlines, they do not announce their schedules too far in advance. I would expect them to have their summer schedule no later than March, if not before. Booking it at home before you leave will be cheapest. Try Skyscanner.net for ATH-PAR which will find Easyjet and any other low-cost airline that might be on ATH-PAR this summer. Sometimes even the big airlines try to compete on price, so Olympic, Air France (maybe even Aegean?) might have a good offer once you get closer to Spring-time. Of course that won’t be much issue if Air Transat decide to serve Athens again next summer—that could make your flight back to Canada from Greece much easier than having to back-track to Paris first.